The present invention relates to a process chamber in connection with a circulating fluidized bed reactor for utilizing internal or external circulation of solid material or both in heat transfer purposes. Said process chamber is located inside the furnace of the circulating fluidized bed reactor adjacent to at least one of the furnace walls, and the interior of said process chamber is provided with fluidized bed heat exchanger means for heat transfer from the solid material to heat transfer medium inside the heat exchanger means.
Fluidized bed heat exchangers (later on abbreviated as FBHE's), which transfer heat between bed of fluidized particulate solids and heat transfer medium, have been in use for many years and in many appliances.
A circulating fluidized bed reactor (later on abbreviated as CFB) comprises a furnace and at least one particle separator which are connected together. A particle separator separates solid particles from flue gas--solid particles suspension entering the separator from the upper part of the furnace. Separated solids are recycled back to the lower part of the furnace via separator and loopseal. This solid circulation is called external circulation, later on EC. In addition to vertical upflow of flue gas and solid particles in the furnace entering the separator inlet, there is a vertical downflow of particles near the furnace walls. This solids circulation is called internal circulation, later on IC.
FBHE's in circulating fluidized bed reactors can be either internal or external type or both, depending on whether the FBHE is utilizing the particles of internal and/or external circulation. A typical CFB process feature is that external circulation of solid material decreases rapidly when load decreases, with the result that heat transfer in the FBHE can become inadequate. Systems with FBHF's in contact with both internal and/or external particle flow streams have been developed to solve that problem.
In CFB reactors, FBHE process chambers can be integrated with the furnace walls and FBHE can be constructed by using bent tubes. The location of an integrated FBHE process chamber can be anywhere from the lower part to the upper part of the reactor furnace, and may be either inside or outside of the furnace walls.
FBHE process chambers located inside the lower part of the furnace can be open in the top part to allow internally refluxing particles to flow into the FBHE process chamber downwards along the furnace walls as suggested by Chambert according to U.S. Pat. No. 5,060,599. Further it is possible according to Chambert to arrange the site of the construction so that particles from the cyclone outlet loop seal can also spill into the same FBHE process chamber.
Furthermore, Hyppanen in accordance with U.S. Pat. No. 5,332,553 suggests a FBHE process chamber in which the roof of said FBHE process chamber is provided with holes or screens for classifying particles before they can enter the FBHE process chamber. However, this kind of roof construction with hole s or screens has the disadvantage that screens can be blocked (or eroded) by heavy solids flow, and especially by fuel and coarse particles splashing from the main fluidized bed because said FBHE process chamber is located inside the reactor furnace at the lower part of the same.